Recently, the electric motor vehicles are attracting attention because they will solve various problems due to the exhaust gas from internal combustion engines which are used for gasoline automobiles. More specifically, carbon dioxide which is contained in the exhaust gas form internal combustion engines accumulates and concentrates in the atmosphere, causing the greenhouse effect and air pollution which are serious problems against the global environment. As a next-generation vehicle which radically solves these problems, electric motor vehicles using a drive motor which does not produce exhaust gas are being put into practical use and various proposals are being made.
But, this drive source for the electric motor vehicles is a motor which has a high efficiency but produces less heat. Therefore, its heat cannot be used for an air conditioning system unlike enormous waste heat which is produced by the operation of conventional internal combustion engines. In view of this, a heat pump method is generally adopted for the air conditioner of the electric motor vehicle. When this air conditioner is operating, a low- or high-temperature refrigerant which is used to heat or cool the cabin is evaporated or condensed by conducting a heat exchange with the open air by means of an exterior heat exchanger and returned to a compressor, thus being circulated within the system in the same way as a room air conditioner.
In the electric motor vehicle, a regenerative brake which uses the drive motor as a generator is generally used in place of the engine brake of a conventional internal combustion engine. In this case, kinetic energy, which must be reduced when the electric motor vehicle decelerates or goes down a slope, is partly converted into electrical energy by temporarily using the drive motor as the generator, and this electrical energy is recovered into a storage battery, thus the drive motor provides a role of an auxiliary brake.
For this type of electric motor vehicle, a lead storage battery is generally used broadly in view of its cost and good resource balance. But, the lead storage battery has disadvantages that its performance is deteriorated and the service life is heavily ruined when the battery, which still has a remaining capacity higher than a prescribed level, is quickly recharged exceeding an appropriate charging current for the battery by high regenerative electric power.
For this reason, in the case of a conventional regenerative brake, the generated regenerative electric power is lowered to protect the lead storage battery, and a common foot brake is used to supplement an insufficient braking force of the electric motor vehicle. Other known methods include a method in that excess regenerative electric power which cannot be recovered into the storage battery is lead to a resistor located outside of the cabin to generate heat so as to release the generated heat into the open air, thereby consuming the excess regenerative electric power, and a method in that a flywheel is rotated by the motor which uses the regenerative electric power, thereby saving as mechanical energy in the flywheel.
A conventional electric motor vehicle, however, uses as an energy source a storage battery whose energy capacity is very small as compared with a fuel such as gasoline and, therefore, has disadvantages that a ratio of energy consumed by the air conditioner to the above capacity is high, and when the air conditioner is operated, a mileage per charge is shortened extremely.
Specifically, when the air conditioner of the electric motor vehicle operates to heat the cabin, since it uses a cabin heat exchanger having a smaller heat exchanging capacity than a room air conditioner, to sufficiently heat the cabin by introducing cold fresh air into the heat exchanger, it is necessary to set an operation condition so that a temperature of the refrigerant discharged from the compressor becomes a high enthalpy value and to increase the compressor speed to increase a flow rate of the refrigerant. As a result, the compressor has an increased compression load and an increased rotating speed, so that the air conditioner consumes electric power heavily.
To evaporate the refrigerant which is a gas-liquid mixture into a completely gaseous state and to return to the compressor by the heat exchanger having a small heat exchanging capacity, a very low evaporating pressure value is set so that an evaporating temperature of the refrigerant becomes ten-odd .degree.C. lower than an outside-air temperature, e.g. -10.degree. to -15.degree. C., and a heating degree of 5.degree. to 10.degree. C. is given for complete evaporation. And, to raise a temperature for the heating degree, the flow of the refrigerant is reduced. As a result, the performance factor of a refrigerating cycle is lowered, and the overall efficiency of the air conditioner is lowered.
Furthermore, when this air conditioner is operated for cooling sufficiently by the cabin heat exchanger having a small heat exchanging capacity while introducing outside air of 30.degree. C. or more, it is necessary to make a difference between the refrigerant evaporating temperature and the outside-air temperature large as much as possible. For example, to provide the evaporating temperature of -10.degree. to -15.degree. C., a very low evaporating pressure value is set. As a result, there are disadvantages that a volumetric efficiency is lowered as the compression ratio of the compressor increases, a flow rate of the refrigerant is decreased as a specific volume of the low-pressure refrigerant increases, and a refrigerating capacity at a prescribed compressor speed is lowered, thus the performance factor of the air conditioner is lowered significantly.
In addition, because the heat radiation of an internal combustion engine cannot be used, the electric motor vehicle needs to operate the air conditioner to heat. In a low-temperature environment such as in winter when heating is required, an electrochemical change in the storage battery is inactive, and a charging and discharging capacity of the storage battery is lowered greatly. And, in the low-temperature environment, a heating load in the cabin increases, with the trend increasing the power consumption by the air conditioner. Thus, there are disadvantages that the performance of the storage battery is lowered and the air conditioner consumes huge electric power, so that a mileage per charge is heavily shortened than in any other seasons.
And, when decelerating, since a regenerative braking force of the auxiliary brake is insufficient, a conventional method which requires to use the foot brake at the same time applies a large load to the foot brake and therefore has a problem in view of safety when the electric motor vehicle is running. Furthermore, the electric motor vehicle, which consumes excess regenerative electric power from the regenerative brake by radiation of heat by means of the resistor located outside the cabin, discards the recovered energy partly and has disadvantages that an energy utilization efficiency as the overall electric motor vehicle is low and a mileage per charge is short.
On the other hand, a conventional regenerative system using a flywheel or the like is expensive because a separate motor having a similar capacity to that used for running the electric motor vehicle is required and this device itself is heavy. These points are bottlenecks in putting them into practical use.
In view of the above, this invention is to provide an electric motor vehicle whose actual mileage can be extended by effectively using excess regenerative electric power to improve an energy utilization efficiency of the overall electric motor vehicle.